Re: [uCsimm] Are the uCsimm I/O pins 5V Tolerant?

From: Tom Walsh (tom@mytoys.com)
Date: Wed Jan 26 2000 - 19:08:30 EST


Sam Saprunoff wrote:

> Hello everyone,
>
> I was curious... Are the uCsimm I/O pins 5V Tolerant? I have been unable to
> verify this from searching through the uCsimm manual (Vdd -0.5 to +4.0,
> Vin -0.5 to +7.0), nor the Motorola MC68EZ328 users manual (Vdd/Vin -0.3 to
> +7.0).
>
> Thanks in advance!
>

No, they are not. You must use a logic family such as the 74LV which also provides
for voltage level shifting. Nothing in the 68EZ328 User Manual says anything either
way regarding the voltages on the i/o (and other) pins, as it usually happens,
attaching a voltage higher than that of the the specified supply of A processor,
generally results in damage to the pin through long term use.

I would certainly welcome being wrong on this issue, but as yet, I have read no
definitive documentation that specifically addresses the issue of TTL family
interfacing. Rule of thumb? If they don't spec it, don't believe it!

Regards,

TomW

--
Tom Walsh - WN3L - Embedded Systems Consultant - tom over_at mytoys(.)com
'www.mytoys.com', 'www.openhardware.net', 'www.cyberiansoftware.com'
"Windows? No thanks, I have work to do..."

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